Remote control system



@ct 11945 G. 5. BROWN ET AL REMOTE CONTROL SYSTEM 3 Sheets-Sheet 1 FiledSept. 20, 1941 1,25 wmawwwmm az m L INVENTORS GORDON 8-. BROWN JAY W.FORRESTER Oct. 15, 1946. G. 5. BROWN ETAL I I REMOTE CONTROL SYSTEMFilecI Sept. 20, 1941 3 Sheets-Sheet 2 VARIABLE STROKE i HYDRAULICHYDRAULIC DON 5. BROWN AY W.FORRESTER INVENTORS VARIABLE STROKE PUMPTHEIR AT'TORNEY 6% 1945- G. 5. BROWN- EI'AL 2,409,190

REMOTE CONTROL SYS TEM Filed p 20, 9 1 v 3 Sheets-Sheet VARIABLE.

SPEED so DRIVE AMPLIFIER RECTIFIER INVENTORS GORDON S. BROWN JAY W.FORRESTER I THEIR ATTORNE? Patentecl Oct. 15, 1946 REMOTE CONTROL SYSTEMGordon S. Brown, Wellesley Hills, Mass, and Jay W. Forrester, Anselmo,Nebr., assignors, by mesne assignments, to Sperry Gyroscope Company,Inc., North Hempstead, N. Y.,

ration of New York Application September 20, 1941, Serial No. 411,670

Claims.

This invention relates to systems for remotely controlling positionableobjects, especially objects having considerable inertia such asrotatably mounted searchlights, guns and the like, to cause thecontrolled object to move in correspondence with a controlling object,and it refers, more particularly, to systems of the above character inwhich means are provided to compensate for the normal tendency of thecontrolled object, when following at the speed of the controllingobject, to lag behind the position of the latter object.

One of the difficulties encountered in attempting to provide a system,free from lag, for moving a heavy object in correspondence with a remoteobject is the tendency of such a system to become unstable as the errorin following is reduced, with resulting hunting or oscillation of thecontrolled object. Various types of antihunting control have beenproposed but these arrangements have been for the most part,inconsistent with the elimination of lag. The present invention, on theother hand, provides an inherently stable system to which complete errorcompensation or controllable under or over compensation may be appliedwithout causing a tendency to hunt.

When the controlling and controlled objects are moving at the sameconstant velocity, in a system which employs a control term proportionalonly to positional disagreement as has heretofore been customary, thelag error may be taken to be proportional to this velocity if the effectof the operating condition of the system is disregarded. In this effectare included the results of lost motion, leaks in hydraulic transmissionsystems and resistance to motion of the controlled object. The effect ofthe operating condit-ion of the system, however, in practice i notnegligible and therefore to provide controllable compensation for lagaccording to the present invention, we make use of an auxiliary controlterm or signal, in addition to and in combination with the positionaldisagreement signal, which corresponds to a variable factor soproportioned as to eliminate lag due to all of the above-mentionedcauses. The value of this correction signal, according to the invention,is preferably determined by the position of a member which controls theoutput of the driving motor or other means for moving the controlledobject. This component of control, derived from the position of themotor controlling element, is usually re,- ferred to hereinafter'as avelocity term or signal, since, for-the type of drivingmeans with whicha corpothe present invention is principally concerned, the speed ofvelocity of the driving means and hence of the controlled object isprimarily although not uniquely determined by the position or setting ofthe motor controlling element. To be able to use such a velocity signalor term to eliminate lag we provide first, as has been noted, a systemwhich is stable, that is, one without hunting tendencies and second,means for producing a lag in the response of the controlled.

object to the velocity term as will be further pointed out.

Because of the means adopted, not only is it possible to control theamount of, or entirely eliminate, controlled object lag in our improvedsystem, but it is further possible to cause the controlled cbject tofollow at a constant velocity in a position in advance of thecontrolling object, that is, a lead of adjustable amount may beintroduced. This is a feature particularly applicable to many types ofgun positioning systems, for example, systems where the controllingobject is a telescope or sight by means of which a moving target istracked and it is required that the gun be advanced ahead of theposition of the sight to compensate for target movement during the timeof flight of the projectile or to introduce other corrections needed insuch systems.

In addition to eliminating positional disagreement or lag as a functionof the velocity of the controlled object, it is possible by the controlmeans of the improved system to eliminate positional disagreement or lagdue to variations in torque which the controlled object may impose onits driving means. That such a lag can exist even under zero-velocityconditions is evident from the fact that the driving motor may requiredthe maintenance of a certain rate of supply of motivating medium merelyto hold the controlled object in the desired position against a countertorque or load. This torque-correction feature, like the elimination ofvelocity lag, is important in gun positioning systems, where it isnecessary to hold the gun trained on the target under varyingconditions, such as where the gun is exposed to a heavy cros wind, orwhere the gun base is not horizontal, so that a non-uniform load may beimposed on the gun driving means.

In the embodiments of the invention illustrated in the drawings, certainelements are shown in electrical, mechanical and hydraulic form and areso described. It will be apparent to those skilled in the arthowever,.that a wide choice is presented as to the elements which can beused to perform the described functions and that systerns within thescope of the invention may utilize equivalents of widely diiTerenttypes.

One object of the invention is to provide'an error-free remote controlsystem for objects possessing substantial inertia.

Another object is to provide an inherently stable system for causing acontrolled object to follow the motion of a remote controlling objectand one which may be made error-free Without thereby becoming subject tooscillation or hunting.

Another object is to provide a system of the above character in whichthe driving means for the controlled object is actuated jointly inaccordance with the positional disagreement of the controlling andcontrolled objects and in accordance with the position or setting of thespeed control for said means.

A further object is to provide a system of the above character in whichthe actuation of the controlled object driving mean in accordance withsaid control setting is controllably delayed to adjust the relativephase of the positional and speed control terms.

Another object is to provide a control system which permits driving thecontrolled object selectively in positional agreement with or lagging orleading the controlling object by an adjustable amount.

Another object is to provide a control system in which the controlledobject position is main tained in synchronism with or leading or laggingthe controlling object position by an adjustable amount for any torqueexerted upon the controlled object, whether such torque be great orsmall.

Still another object is to provide a system of the above character inwhich a plurality of controlled objects may be positioned by a singlecontrolling object substantially without reaction one upon the other orupon the controlling object.

Other objects and advantages of this invention will become apparent asthe description proceeds.

In the drawings:

Fig. l is a diagram of a control system in accordance with our inventionin which certain members are shown in section.

Figs. 2 and 3 are diagrams illustrating modifications of the system ofFig. 1.

Fig. 4 is a schematic diagram for purposes of explanation.

Fig. 5 is an enlarged sectional view of a lag controlling device.

Fig. 6 is a schematic diagram showing a modification in the electricalpositional control system.

In Fig. 1, reference numeral i is applied to a controlling object Whosemotion is to be reproduced at a remote point, which object is hereillustrated simply as a handwheel but may be a tracking telescope orother movable member. Controllin object I rotates shaft 2 which mountsthe three-winding rotor 3 of Selsyn transmitter t having a statorwinding 5 excited from an alternating current source 6. The windings ofrotor 3 are connected by three conductor transmission line I to similarwindings of th movable or rotor member 8 of electrical difierential 9also having a similarly wound stator member iii. The windings of statori9 are connected by three conductor transmission line l2 to the windingsof rotor E3 of Selsyn receiver l4 having a stator l5 excited from source6. Rotor I3 is mounted on shaft 16 connected by gearing ii to thecontrolled object, here illustrated as rotatable platform I 8 mountingturns.

gun i8. It will be obvious that any other heavy object may be similarlyarranged for controlled movement.

Selsyn transmitter 4 and receiver H; are similar to instruments commonlyused in position reproducing systems but are here used to generateelectrical signals proportional to the relative position of theirrespective rotors. Electrical differentials, such as differential 9,having a construction similar to Selsyn instruments are well known inthe art and need not be described here. In'the operation of such devicesthe rotor tends to align the magnetic axis of its field with that of themagnetic axis of the field of the stator and in consequence is adaptedto exert a torque proportional to any misalignment of the directions ofthe two fields, which in the present system represent the positions ofthe controlling and controlled objects respectively, by virtue of thesignals generated by Selsyns 3 and I4. Rotation of rotor 3 is opposed bya counter torque applied by springs II and H about pivot point 22 aswill now be described.

Springs H and H resiliently connect levers I9 and 223. Lever I9 ispivoted to datum at 2| while lever 28 is connected to and rotates withdiiferential rotor 8 about pivot point 22. Springs H and l i being onopposit sides of the pivot point are adapted to oppose rotation of lever20 in either direction and thereby to supply a torque to balance anytorque developed magnetically between rotor 8 and stator Iii. Lever 29is pivotally connected at one end to piston rod 23 of pilot valve E iwhose displacement furnishes the input to a hydraulic amplifying system.Valve 2s comprises a housing 25 having a cylindrical bore in whichsleeve 25 is slidable, and within the sleeve a piston assembly,comprising pistons 21, 28, 25 and 3%] formed on rod 23, is slidable.Pistons 28 and 2e cooperate with and govern the effective openings ofports 3! and 32, respectively, in sleeve 26 while pistons 2'! and 39close the bore of sleeve 28 to prevent loss of fluid.

A motor 33 drives pressure pump 34 which supplies fluid, preferably oil,from sump 35 through check valve 35 to valve 2 3 by way of intake pipe38, the return fluid flow from the valve to the sump being by way oftail pipe 3?.

Pipe 38 communicates by way of port 39 in sleeve 2% with the bore ofsleeve 28 to supply fluid which normally exerts equal pressure inopposite directions on pistons 28 and 29.. In their equilibriumpositions these pistons completely cover and slightly overlap ports 3!and 32 in sleeve 26, respectively, which communicate with annulargrooves at and M on sleeve 26, respectively, which in turn communicatewith pressure pipes 42 and 3, respectively, conecting with cylinder 44on opposite sides of piston 55. The return fluid from the valve andcylinder finds its Way back to tail pipe 31 by way of ports 43 and 41,communicating with annular passage-ways in housing 25 leading to thetail pipe.

Piston 55 is mounted on piston rod 48 and the motion of this piston,communicated by rod 48, tilts cylinder block 49 of multi-cylinder,variable stroke pump 50 through yoke 49' which mount the outer bearingin which the block Pump 59) forms one unit of a variable speed hydraulicdrive in which the pump operates hydraulic motor 5! at a speed dependenton the stroke of its pistons which in turn is proportional to the angleof tilt of the cylinder block. This combination of pump and motor iswell known in the art under the name of the Vickers variable speed driveand will not be described in detail. Cylinder block 49 of the pump,constantly driven by motor 55' and housing cylinders 52 in which pistons53 slide when the block is rotated about an axis at an angle with theshaft of driving motor 55, is pivoted by yoke 49' about hollow trunnions54 and is angularly adjustable about said trunnions in accordance withthe position of piston rod 48. Fluid displaced by the pump pistons iscirculated to hydraulic motor 5| by way of trunnions 54 throughlines 55and 56 and motor 5| is connected to drive platform I8 by way of shaft 51and shaft it connected to shaft 51 by gearing H.

Piston rod 48 extends through cylinder 54 at both ends and at the lowerend is articulated through link 58 to rotate lever 59, pivoted at 65 toarm 6|, through a pivot connection at the right end of the lever. At itsleft end lever 59 is pivotally connected to valve sleeve operating rod62 which axially displaces sleeve 26 within housing 25 to effect achange of registry between ports 3| and 32 in said sleeve and pistons.28 and 29 on rod 23.

Arm Si is not fixed to datum but is given a small longitudinaloscillation by "dither motor 63 slidably mounted on base 64 andadjustable along this base by means of adjustment screw 65. Motor 63mounts on its shaft an eccentric 66 which cooperates with slotted. link61, pivoted to datum at 68, to oscillate arm 51, the amplitude of thisoscillation or dither being determined by the position of eccentric 66relative to pivot $8. The oscillation imparted to arm 5i is transmittedto sleeve 26 through lever 59 and rod 52, piston as being substantiallyheld against direct oscillation by fluid pressure.

The dither introduced by motor 63 preferably has a frequency in theneighborhood of about 30 to 60 cycles per second and an amplitude of afew thousandths of an inch. With dither eccentric 66 stationary, pistons28 and 29 normally overlap ports 3! and 32, respectively, by a fewthousandths of an inch. The actual magnitude of the dither should besuch that sleeve 26 oscillates along its axis by an amount slightlygreater than the port overlap so that ports 3! and 32 in sleeve 25 areopened at each extremity of the oscillation just sufficiently to admitfluid cyclically to the piston 45 in quantities suitable to ditherpiston 45. The purpose of this dither feature is to break seizures ofrelatively movable contacting surfaces due to static friction and toremove dead zones in the system from valve piston rod 23 as far back asthe output shaft H? of the hydraulic transmission. In other words,sufficient tremor is imparted to piston 5.5 to impart some (although alesser) tremor to pump and also to transmit suficient tremor through tomotor 5i to take up any lost motion in gearing I! and H, in addition toovercoming static friction throughout the system. Therefore by impartingthe correct amount of tremor to the system, we materially improve itsresponse characteristics, and eliminate errors due to lost motion.

Piston rod 48 at its lower end mounts a bracket 69 connected by spring12 and piston rod 13 to piston 70 moving in dash-pot 1!, spring 12 beingof a type adapted to sustain either tension or compression. Dash-pot His filled with viscous fluid which is pumped back and forth between theopposite ends through a conduit 14 having a restriction to introduce afriction factor and thereby regulate the speed of response of the motionof the system Ill, 12, 13 to a displacement of bracket 69. A preferredconstruction of said restriction is shownin Fig. 5 which illustrates theuse of a plurality of spaced thin discs 15 each closing conduit 14except for a small orifice 15. The several orifices 15' are in staggeredrelation so that the damping fluid is forced by a tortuous path throughthe conduit and passes through a multiplicity of" orifices. As anexample of the dimensions of a practical device, diameter discs .002"thick have been used having orifices .035" in diameter. Thin-edgedorifices of this type allow orifice flow which is substantiallyindependent of temperature. The friction introduced by such anarrangement is variable by varying the number of discs, the size of theorifices and to some extent the staggering and spacing. Means are thusprovided for introducing a friction factor of predetermined magnitude.

Piston rod 13' is pivotally connected to one end of lever 16, rotatableabout adjustable pivot point 11, and the opposite nd of lever 16 ispivotally connected to one end of arm 18, which in turn is pivotallyconnected at its other end to lever ill at pivot point I9.

In operation, angular displacement of handwheel 1, by creating adisagreement between the positions of selsyn rotors 3 and i3 at the twoends of the system, relatively displaces the directions of the resultantfields of rotor 8 and stator it) of fselsyn differential 9 and therebycauses rotor 3 to exert a torque tending to tilt lever as about pivotpoint 22. This torque is resisted by the counter-torque exerted bysprings H and I i about pivot point 22, the result being a limitedrotation of lever 28, the magnitude of which is determined by the ratioof the spring torque (i. e., the strength of the springs times theirlever arm) to the torque exerted by electrical differential 9. Rotationof lever 2!] moves piston rod 23 and displaces pistons 2E and 29 touncover ports 3! and 32, respectively, and thereby differentially changethe fluid pressure on opposite sides of piston 45, causing said pistonto move Within cylinder 34 and, through piston rod 48, change the angleof tilt of cylinder block 49. The resulting change in operating speed ofhydraulic motor 5| is in a sense which tends to restore the positionalagreement between the controlling and controlled objects and hence towipe out the signal generated by the positional disagreement betweenrotors 3 and IS.

The motion of piston 45, transmitted by rod link 58, lever 59 and rod 52to sleeve 26, so positions the sleeve that ports 3! and 32 are returnedto their normal relationship with respect to pistons 28 and 29. Theconnection between piston 45 and sleeve 26 therefore constitutes therepeat-back which wipes out the input to the hydraulic amplifying systemapplied by way of rod 23.

'At the same time that the motion of piston 45 is transmitted to sleeve23 it changes the extension of spring 12 and thereby exerts a torque onlever 18 about pivot point 1'! which, if unopposed would cause link 18to exert a corresponding torque on lever l9 about pivot point 2|.However, dash-pot I! being filled with viscous fluid which, to allowmovement of piston 15, must be pumped through orifices 15 in conduit 14,movement of piston 15 is initially retarded and is completed only aftera certain adjustable time interval- Change of displacement of piston 45is thus transmitted after a delay to lever 19, where, by

the coupling of springs H and H, the resultingtorque is effectivelycombined with the torque exerted by rotor 8 on lever 23. Sincedisplace-- ment of piston 45 is proportional to the angle of tilt ofcylinder block 49 and hence, for a given operating condition, to thespeed at which hy draulic motor drives platform Hi, the system comprisesmeans for combining with a signal proportional to the positionaldisagreement of .a controlling and a controlled object a signalprimarily proportional to the velocity of the controlled object, thecombination occurring in an adjustable phase relationship. The sense inwhich the two component signals are combined is significant. Theso-called velocity term as defined herein is here applied in aregenerative sensewhich causes it to take over, Wholly or in part, thefunction of the displacement or positional disagreement term insupplying a control signal to keep the driving means operating atconstant velocity. Thus the system may be caused to operate at constantvelocity with decreased lag or without any disagreement of the twoobjects, if so desired, or, by increasing the magnitude of the velocityterm, to operate with the controlled object leading the controllingobject.

It should be noted that the extent to which the displacement of piston45 is not proportional to the speed of the hydraulic motor (because ofany torque applied to and resisting motion of platform if; or because ofoil leakage in the pump and motor system of the Viclzers transmission)in.

no way prevents the controlled object from following the controllingobject in the manner desired. This is readily seen by noting that,should a particular operating condition call for additional displacementof piston 45, the additional displacement is supplied by an additionaldisplacement of arm initially by virtue of error between elsyns and i l,but eventually by displacement of arm l9 resulting from displacement ofpiston 25. Thus again, a displacement of lever l9 resulting fromdisplacement of piston 45 has taken over, wholly or inparw-whichever isdesired-the function of the displacement or posi- .1

tional disagreement term in systems of the usual type so that the systemof the present invention operates at constant velocity or at rest in thepresence of different load torques without disagreement of the twoobjects, or with the controlled object leading or lagging thecontrolling object by a predetermined amount, as desired.

Fig. 4 is a purely schematic simplified diagram of the system of Fig. 1on which are designated the constants whose relationships determine thestability of the system and the error or absence of error in thefollowin of the controlled object. Rotor 8 and stator ll of difierential9 are shown connected by a virtual spring 9', having a stiffness k3representing the torque exerted per degree of misalignment of the statorand rotor fields. Lever 28' corresponding to lever 26 of Fig. 1 isrotated about pivot point 8! by rotation of rotor S. he equivalentstiffness of the virtual spring 9, manifested at the end of lever 28,may be taken as ks where If 12 is assumed to have a length equal tounity, then ks' ks. Spring H", having a stiffness R2, represents acombination of springs H and Ill while 705 is the stifiness of spring"l2. Lever l6" pivoted to datum at 82 replaces levers wand 9. Thedistances from the connection points of 8 springs I I" and 12' to pivotpoint 82 are 15 and la, respectively. The damping coeflicient of theresistance to motion of piston H1 in dash-pot 1| is f1. schematically,motion of the piston 45 which directly affects speed control rod 48 isshown as being also transmitted to one end of lever 59 (corresponding tolever 59) the other end of which reciprocates sleeve 26, thusillustrating an arrangement adapted to provide a ratio between themovement of the piston and sleeve.

For purposes of analysis two ratios will now be defined:

If 1 i]: assumed to have a length equal to unity, then kg 3.

displacement of piston rod 48 b displacement of valve rod 23 (assumingpivot point 8| to be at the center of lever 20), and

For zero error the relationship of the system constants must be suchthat The derivation of this expression is as follows: If a: be adisplacement of the pilot valve rod 23, then be: is the correspondingdisplacement of lever 76' at distance 15 from the pivot, and dy willthen represent the displacement of lever '56 at a distance Z3 from thepivot 82. The forces acting on lever 16' may be equated as follows:

Since the derivation is concerned with equilibrium conditions underconstant velocity operation, the effect of the dashpot ma bedisregarded.

Dividing (2) by 13 and separating terms in a:

The forces which act on lever 20' may be expressed as Where e=angle ofmisalignment of magnetic axes of synchro differential due to an errorbetween controlled and controlling object.

Substituting (4) in (5),

If e is to equal zero for all cases of constant velocity operation, thenta e o which may be solved explicity for b, as in (1) above. v

In order that the controlled object may follow the controlling object ata constant velocity but at an angle of lead: the value of b should begreater than that for zero error as defined above 9 and conversely foran angle of lag it should be less.

Stability in our improved system is best achieved by first making theresponse of that part of the system which comprises valve 24 and piston65 so rapid that it can faithfully follow incipient oscillations in thatpart of the system which comprises the selsyn instruments and theconnected load, second b choosing spring constant k2 so that itsrelation to the spring constant 103, the characteristics of thehydraulic transmission, and other constants of the system, provides astable system having rapid response and third by applying the so-calledvelocity signal in proper phase by adjustment of the dapming introducedby motion of piston 10. When the constants of the system fulfill theabove conditions no oscillation can build up and we are free to make thesystem errorless for constant velocity following. Previously proposedsystems have not provided this rapid response in combination with theproper phasing of a velocity control and hence could not effectivelyneutralize incipient oscillations and prevent their building up.

The modification of Fig. 2 illustrates a system generally similar tothat shown in Fig. 1 except that dash-pot H is connected directly tolever 19 instead of through the spring '62 and the linkage shown inFig. 1. This is a simplification which permits the construction of astable system in which, while all error cannot be eliminated, thecontrolled object is capable of operating at a very small angle of lagwhich may be satisfactory for many purposes. Specifically thismodification of the invention provides a system in which th lag, orerror in following, which exists when arm I9 is stationary in itscentral position, is reduced by an amount given b the ratio since 762may readily be mad at least four times as great as 703 it follows thatthe lag, or error in following (at constant velocity) may be reduced bythe arrangement of Fig. 2 by at least 80 per cent. As a furthersimplification conduit 1!! may be eliminated and piston 10'corresponding to piston 10 Fig. 1, provided with a plurality ofpassageways at through which fluid is pumped from one end of thecylinder to the other. These passageways may be of desired area to givea predetermined value to the frictional constant ii.

In the operation of the modification of Fig. 2,

when rotor 8 exerts a torque on lever 26 due to trolled object isintroduced into the system electro-mechanically instead of my mechanicalmeans only as in the arrangement of Fig. 1. In Fig. 3 piston 10 isdriven from piston rod 48 through adjustable ratio lever 69 and spring12 and its displacement is communicated to rotatable member l5 of selsynl4 (which takes the place of previously described stator l5) by way ofrack and pinion and gearing 86 and 81. In this arrangement member I5, isrotated to vary the angular position of its magnetic field,

the variation thus introduced causing a misalignment of the fieldsofselsyn s 4 and M at the sending and receiving ends, respectively, andthereby a misalignment of rotor and stator fields of differential 9. Anadditional torque thus exerted on levers l9 nd 29 in a manner generallysimilar to the additional torque exerted upon these levers by arm E8 ofFig. 1.

While the velocity'term is shown as being introduced through therotation of one of the members of selsyn 14, it will be apparent thatthe same effect may be produced by the rotation of one of the pair ofrelatively movable members of either selsyn or differential 9, theresult in any case being the misalignment of two magnetic fields of a'device which directly or indirectly causes an input signal to besupplied to valve 25 with a resultant change in the output of thehydraulic motor.

Fig. 6 illustrates in the schematic form of Fig. 4 a modification of theinvention in which. the input to the hydraulic drive proportional to thepositional disagreement of thev controlling and controlled objects issupplied by a special torque motor actuated by a signalgenerated by thereceiving end selsyn, the signal being preferably amplified andrectified, for example, in an electron tube amplifier. Selsyn A isexcited from source 6 as in the previously described arrangements butthe windings of its rotor 3 are directly connected by three conductortransmission line IE to the rotor windings of the remote selsyn itinstead of to an intermediate electrical differential. The rotor l3 ofselsyn i being driven in positional agreement with the controlledobject, the stator l5 receives a reversible phase E. M. F. proportionalin magnitude to the positional disagreement of the two objects, as iswell known in the art of positional control systems, which signal isapplied to the input of a balanced amplifier-rectifier 90 whose D. C.output excites torque motor 9|. Amplifier fill is preferably of a knowntypehaving a split or push-pull output circuit, such as is shown, forexample, in the pending application of C. Frische et al., forElectro-hydraulic control system, Ser. No. 284,642, filed'July 15, 1939.

Motor 9| comprises pole pieces 92 of a magnet assembly supplying fluxtoa gap in which armature 93 is located. Armature 93 carries split coil96 (or its equivalent, two connected coils) having two'extern'alterminals and a center tap all connected to the split output circuit ofamplifier 94, the two halves of the coil being respectively connected tothe two halves of the output circuit. Armature 93 is mounted on shaft 85by means of which it is capable of exerting a torque on lever 20' in.the manner of rotor 8 of differential 9.

In operation, potential disagreement of the two objects creates an A. C.signal voltage in stator winding [5 proportional to the disagreemeritand phased according to its sign, i. e., according to whether a lag orlead in following exists. When no signal is applied to the input ofamplifier 90 substantially equal rectified current flow in the twohalves of winding 94, the effects of which, due to the coil connections,neutralize one another (or the amplifier may be operated so thatnormally no current flows in either half of the coil). Upon theapplication of an input voltage to amplifier 98 a differential change ofcurrent occurs in the two halves of coil and a torque is created by theinteraction of the permanent field due to the pole pieces and theunbalanced armature field thus created The sense 'of the differentialchange of output and hence of the torque exerted by the rotor isdetermined by the phase of the amplifier input, which in turn depends onwhether a lag or lead exists, and thus the torque exerted on lever 2'5by rotor Q3 can be made to apply an input to the hydraulic transmissionof the proper sign to restore positional agreement between the twoobjects. By proper design, also, the torque exerted by motor 91 can bemade closely proportional to the difierence of the currents in the twohalves of its armature winding, which in turn is readily madeproportional to the signal input to amplifier $33. Other means includingA. C. excited torque exerting devices may be employed to supply a torqueproportional to error in following. One of the important advantages ofthe arrangement of Fig. 6 over the arrangements previously described isthat very little power is required as an input to amplifier 9B incomparison with the power which must be delivered to differential Q, forexample, to cause it to exert the required torque on lever 26. Thisconsiderablyimproves the operation of the system and permits the controlof a number of separate objects from a single controlling object withoutthe behavior or position of one controlled object seriously affectingthe behavior or position of any of the other objects or causingsubstantial reaction on the controlling object. An important applicationof our invention resulting from this feature is the control of a batteryof guns, or other movable objects of substantial inertia, by -a singlecontrolling element, such as a sighting telescope.

In Fig. 6 there is shown a three-conductor transmission line $6branching off from line [2. This-branch line is adapted to be connectedto the rotor winding of a second Selsyn signal generator similar toselsyn l4 and if the rotor of this second selsyn be rotated incorrespondence with a second controlled object. a system similar in allrespects to the one shown and described in detail, including the drivingand other associated means, may be added, the controlling object andtransmitter being common to the two systems. To simplify'the figure onlythe transmission line to the receiving selsyn of the second system isindicated.

Since the signal taken from this receiving or controlled object selsynoi the second system will preferably be applied through an amplifiersimilar to amplifier 9D and since only a very small amount of power istransmitted over the common line to supply the inputs to the amplifiersthere will be relatively little coupling between the separate systems.To further reduce interaction between the receiver selsyn, resistances9! and 98 may be inserted in the lines respectively feeding theseselsyns after the point at which the lines branch from the commoncircuit. A considerable number of receiving selsyns may beinterconnected in the described manner without reaction and employed assignal generators in a corresponding number of systems according to ourinvention.

As many changes could be made in the above constructionand manyapparently widely difierent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained'in the above description or shown in the accompanying drawingssha l be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure byLetters Patent is: I

1. A positional control system comprising a controlling object, acontrolled object, a variable speed drive for actuating the controlledobject, error-measuring means responsive to differences in positionbetween controlled and controlling objects for generating an errorsignal as a function of said disagreement, an amplifier having itsoutput in control of the variable speed drive and having its inputconnected to the error-measuring means, and a regenerative feedbackconnection from the amplifier output to the amplifier input, saidfeedback connection including means for delaying transmission to theinput of the effect of changes in the output.

2. A positional control system comprising a controlling object, acontrolled object, a variable speed drive for actuating the controlledobject, a speed control for said drive, error-measuring means responsiveto differences in position between controlled and controlling objectsfor generating an error signal as a function of said disagreement, anamplifier having its output connected to the speed control of thevariable speed drive and having its input connected to theerrormeasuring means, and a regenerative feedback connection from thespeed control to the amplifier input, said feedback connection includingmeans for delaying the effect at the amplifier input of changes in thespeed control.

3. A positional control system comprising a controlling object, acontrolled object, a variable speed drive for actuating the controlledobject, error-measuring means responsive to differences in positionbetween controlled and controlling objects for generating an errorsignal as a function of said disagreement, an amplifier having itsoutput in control of the variable speed drive, a regenerative feedbackconnection from the amplifier output for supplying a signal related tothe speed of the controlled object, means for combining the error andthe regenerative feedback signals and for supplying the combined signalto the amplifier input, and means associated with the feedbackconnection for delaying the effect at the amplifier input of changes inamplifier output.

4. A positional control system comprising a controlling object, acontrolled object, a variable speed drive for actuating the controlledobject, a movable control element in control of said drive to vary thespeed thereof, error-measuring means responsive to differences inposition between controlled and controlling objects for generating anerror signal as a function of said positional differences, an amplifierhaving its input responsive to the error signal and its output connectedto the movable control element of the variable speed drive, and aregenerative feedback connection between the movable speed controlelement and the amplifier input for supplying to said input a signalbased on the position of the speed control element, said feedbackconnection including means for delaying transmission to the amplifierinput of changes in position of the speed control.

5. A positional control system comprising a controlled object, acontrolling object, a variable speed drive for actuating the controlledobject, a speed control for said drive, error-measuring means responsiveto differences in position between confrolled and controlling objectsfor generating an error signal as a function of said d sagreement. anamplifier having a power output member connected to the speed controlfor the 13 variable speed drive and an input member connected to theerror-measuring means, and a resilient regeneratively-connected feedbackconnection between the power output member of the amplifier and theinput member, said feedback connection including means for delaying theresponse of the input member to changes in position of the speedcontrol.

6. A positional control system comprising a controlled object, acontrolling object, a variable speed drive for actuating the controlledobject, a speed control for said drive, error-measuring means responsiveto differences in position between controlled and controlling objectsfor generating an error signal as a function of said disagreement, anamplifier having a power output member connected to the speed controlfor the variable speed drive and an input member connected to theerror-measuring means, and a regeneratively-connected feedbackconnection between the speed control member and the amplifier input,said connection including a movable member, damping means therefor, andresilient connections between the movable member and the speed controland between the movable member and the amplifier input.

7. A positional control system comprising a controlled object, acontrolling object, a variable speed drive, for actuating the controlledobject, a speed control for said drive, error-measuring means responsiveto differences in position between controlled and controlling objectsfor generating an error signal as a function of said disagreement, anamplifier having displaceable input and power output devices connectedrespectively to the error-measuring means and to the speed control,resilient means cooperating with the error-measuring means and theamplifier input device for controlling the response of the latter to anerror signal, and a regenerative feedback connection from the amplifieroutput to the resilient means for modifying the control action thereofon the amplifier input device in accordance with the setting of thespeed control of the variable speed drive, said feedback connectionincluding means for delaying the effect at the resilient means ofchanges in setting of the speed control.

8. A positional control system comprising a controlled object, acontrolling object, a variable speed drive for actuating the controlledobject, a speed control for said drive, error-measuring means responsiveto differences in position between controlled and controlling objectsfor developing a force as a function of said disagreement, an amplifierhaving displaceable input and power output devices connectedrespectively to the error-measuring means and to the speed control,resilient centralizing means connected to the amplifier input device,said centralizing means being adjustable, and a regenerative feedbackconnection from the amplifier output for adjusting the centralizingmeans in accordance with the position of the speed control, saidconnection including a damped resilient connection between thecentralizing means and the amplifier output for delaying the response ofthe centralizing means to changes in the setting of the speed control.

9. A positional control system comprising a controlled object, avariable speed drive for actuating the controlled object, a movablespeed control element in control of said drive, errormeasuring meansresponsive to differences in position between controlled and controllingobjects for generating an error signal as a function of said positionaldisagreement, means including a hydraulic amplifier for actuating themovable control element of the variable speed drive, said amplifiercomprising a pilot piston connected to the error-measuring means, apower piston connected to the movable element in control of the variablespeed drive, a pilot piston sleeve, a repeat-back connection from thepower piston to the pilot piston sleeve, and a regenerative feedbackconnection from the power piston for supplying a. signal based ondisplacement of the speed control element, said feedback connectionincluding spring and dashpot means for delaying transmission of saiddisplacement signal, and means for combining said error and displacementsignals and for actuating the pilot piston in accordance with thecombined signals.

10. A positional control system comprising a controlled object, acontrolling object, a variable speed drive for actuating the controlledobject, a movable speed control element in control of said drive,error-measuring means responsive to differences in position betweencontrolled and controlling objects for generating an error signal as afunction of said positional disagreement, means including a hydraulicamplifier for actuating the movable control element of the variablespeed drive, said amplifier comprising a pilot piston connected to theerror-measuring means, a power piston connected to the movable elementin control of the variable speed drive, a pilot piston sleeve, arepeat-back connection from the power piston to the pilot piston sleeve,and a regenerative feed-back connection from the power piston to thepilot piston, said feedback connection including a movable member,damping means therefor, and resilient connections between the member andthe power piston and between the member and the pilot piston.

GORDON S. BROWN. JAY W. FORRESTER.

